This present application relates to cylindrical nonaqueous electrolyte batteries, particularly to cylindrical nonaqueous electrolyte batteries that have high resistance to external impact.
There is a strong demand for long-lasting batteries in response to the constant developments of thin, small, and light-weight portable electronic devices designed for cordless and portable electronic devices such as cellular phones and laptop personal computers. The most common variation of such batteries is the cylindrical lithium ion secondary battery.
Generally, the cylindrical lithium ion secondary battery is constructed from a wound electrode unit and a nonaqueous electrolytic solution, the former being a multi-layer roll of an electrode laminate of a positive electrode, a negative electrode, and a separator sandwiched between the positive electrode and the negative electrode. The positive electrode has a positive electrode active material layer formed on the both sides of a belt-like collector, and the negative electrode has a negative electrode active material layer formed on the both sides of a belt-like collector. In this type of wound battery, an adhesive member is provided at the electrode laminate end portions (the cut end portions of the positive electrode collector, the negative electrode collector, and the separator), specifically, at the terminating end of the electrode roll, so that the electrodes do not become loose. The adhesive member is provided in way that covers the positive electrode end portion and the negative electrode end portion.
The wound electrode end unit with the end portion covered with the adhesive member is inserted into a cylindrical battery canister having an open end. To make the insertion of the wound electrode unit easier, a certain clearance is required between the outer diameter of the wound electrode unit and the inner diameter of the battery canister.
However, in the event where a battery with such a clearance is dropped or subjected to some other external impact such as vibrational impact, the wound electrode unit tends to flow or rotate inside the battery canister. Such movement of the wound electrode unit translates into a force that is exerted on the positive and negative electrode terminals connected to the wound electrode unit. This may cause damage to the welded portion between the positive electrode terminal and the safety valve provided on the battery lid, the welded portion between the negative electrode terminal and the bottom of the battery canister, and the part of the negative electrode terminal attached to the negative electrode collector. Further, fracture or other damage to the positive electrode terminal and/or the negative electrode terminal may lead to breaking in the battery internal circuit. The problem of a flowing wound electrode unit in the canister, and the resulting damage to the welded portions of the electrode terminals that leads to the breaking of the battery internal circuit is also present in rectangular lithium ion secondary batteries, though the electrode assembly is less likely to rotate.
As a method of preventing the rotation or flow of the wound electrode unit as described above, it has been proposed to reduce the clearance between the wound electrode unit and the canister by attaching to the wound electrode unit a material that swells upon absorbing the electrolytic solution. Heat-resistant films are also available that are provided as the laminates of a fluororesin layer and other resins, as proposed in JP-A-2005-169935 (Patent Document 3), JP-A-2005-59409 (Patent Document 4), and JP-A-2004-255805 (Patent Document 5).